It is well known that two standards of ground vehicles exist. One type is represented by two-wheel vehicles (example motorcycles) that are turned by the operator first countersteering (turning the handlebars slightly in the opposite direction of the desired turn) then leaning into the turn and keeping the center of gravity in the plane of the apparent vertical due to combined gravitational and centrifugal forces. Lean angle is determined by speed and turn radius, i.e. the faster the speed and the tighter the turn radius the more the operator is required to lean the motorcycle while turning. This lean also serves to stabilize the motorcycle throughout the turn.
The other type is represented by vehicles with stationary stability, such as three-wheeled vehicles (example motorized tricycles) or four-wheeled vehicles (example automobiles). These vehicles steer by turning the front wheel(s) by way of handlebars or a steering wheel. During a turn centrifugal and gravitational forces combine to force the vehicle toward the outside of the turn. If the forces become too great the vehicle can roll over. This is a greater potential problem in a three-wheeled vehicle that has two rear wheels and only one front wheel situated in line with the vehicle's centerline.
An independent rear suspension provides a far better quality and more comfortable ride for the operator and passenger particularly when travelling over a bumpy or uneven road surface, however when turning hard a three-wheeled vehicle can sway or roll to the outside of the turn as the rear suspension components on the inside of the turn are compressed and the suspension components on the outside of the turn are extended. This body roll shifts the center of gravity to the outside wheel in curves and creates a less stable condition. The sharper the turn and the higher the speed the greater the resulting body roll and the less stable the three-wheeled vehicle becomes. To compensate for this condition, the operator must slow down or the three-wheeled vehicle may tip over. A more rigid non-independent rear suspension design wherein the left and right rear wheels are linked together and can't move independently reduces this effect, however this design results in greater unsprung weight. Whereas movement of suspension components, i.e. their ability to track and maintain traction over bumpy or imperfect road surfaces, is inversely proportional to the unsprung weight rigid non-independent designs will result in a far less comfortable ride for the operator and passenger and can result in the operator and passenger and/or the entire vehicle being bounced around when going over bumps as the bumps are not being absorbed by the vehicle's suspension.
Three-wheeled vehicles have a relatively small front tire contact patch compared to the contact patch of the rear tires. In some circumstances, including wet and other slippery road conditions, the small front tire contact area does not generate sufficient traction to turn the vehicle and the front tire will skid along the road surface and the vehicle will keep going in a straight line. If a larger diameter front tire which has a larger contact patch with the road surface is installed, front wheel traction will be increased however the vehicle will become more difficult to turn due to increased friction from the increased contact patch and increased gyroscopic forces from the increased front wheel mass and will requires greater force from the operator to turn the front wheel. As the vehicle's speed increases the vehicle will become increasingly difficult to turn as the force required to turn the front wheel increases. There is no practical way to attach a powered steering mechanism to the front end of a three-wheeled vehicle that uses a motorcycle style front fork to assist with turning the front wheel and thus make steering easier.
Several designs exist that attempt to improve handling and reduce body roll and make turning easier.
U.S. Pat. Nos. 7,343,997, 7,591,337, 4,064,957, 6,511,078, 6,435,522, 4,487,429, 4,159,128, 6,406,036, 6,328,125, 6,250,649, 6,062,581, 5,169,166, 5,116,069, 5,040,812, 4,974,863, 4,903,857, 4,678,053, 4,660,853, 4,484,648, and 4,088,199 attempt to improve handling, make turning easier and reduce body roll by tilting the three-wheeled vehicle body and/or wheels.
There are several shortcomings of the tilting solution. First, the tilting mechanisms are complicated and have many component parts and are therefore complicated and expensive to manufacture, and can be prone to component failure. Second, any tilting system requires the use of motorcycle tires that necessarily have a rounded profile to enable the motorcycle to lean during turns, however a consequence of this design is that a motorcycle tire has a much smaller contact patch with the road surface than a comparable size automobile tire that is not designed to lean. Automobile tires perform better in drive systems where the two rear wheels are driven by the vehicle's motor, as is the configuration on virtually all three-wheeled vehicles, because they provide better traction due to their flatter profile and resulting larger contact patch with the road surface, are more durable and last longer, and are more cost effective.
A design exists that attempts to reduce body roll and improve handling with a rigid rear suspension design that does not allow the vehicle to lean or squat while turning. This design is intended to minimize flex in the swing-arm and rear-end system and features a differential rear-end with internal solid axles. The swing-arm is a one piece reinforced design, specially constructed to reduce all torsion effects.
The problem with the rigid design that while it eliminates leaning in turns vehicles with this design do not perform well on rough or bumpy roads and provide a poor quality and uncomfortable ride for the operator and passenger for a couple of reasons. First, this design does not allow the rear wheels to move independently of each other making it more difficult for them to follow the contour of the road. Second, the unsprung weight of a suspension system having a solid rear axle is greater than for an independent suspension design and thus further limits the ability of the rear wheels to follow bumps in the road and maintain traction as movement is inversely proportional to the unsprung weight.
It would be advantageous to provide a steering system that provides a comfortable ride for the operator and passenger on a three-wheeled vehicle.
It would also be advantageous to provide a steering system that reduces three-wheeled vehicle turning radius.
It would further be advantageous to provide a steering system that increases three-wheeled vehicle straight line stability.
It would further be advantageous to provide a steering system that improves three-wheeled vehicle high speed handling.
It would further be advantageous to provide a steering system that improves three-wheeled vehicle cornering performance.
It would further be advantageous to provide a steering system that improves three-wheeled vehicle steering response.
It would further be advantageous to provide a steering system that improves three-wheeled vehicle safety.